BACTERIAL GROWTH AND BIOLOGICAL OXIDATION

GENERAL GROWTH PATTERNS IN PURE CULTURES

Bacteria can reproduce by:• binary fission• sexual mode• budding

Growth in terms of bacterial numbers

Phases:• Lag phase – represents the time req’d for the

organisms to acclimate to their new environment

• Log-growth phase – cells divide at a rate determined by their generation time and their ability to process food

• Stationary phase – population remains stationary . Cells have exhausted substrate or nutrients necessary for growth and the growth of new cells is offset by the death of old cells.

• Log-death phase – bacterial death rate exceeds the production rate

Growth in terms of bacterial mass

Phases:• Log-growth phase – There is always an excess

amount of food surrounding the microorganisms, and the rate of metabolism and growth is only a function of the ability of the microorganism to process substrate.

• Declining growth phase – The rate of growth and hence the mass of bacteria decrease because of limitations in the food supply

• Endogenous phase – The microorganisms are forced to metabolize their own protoplasm w/o replacement, since the concentration of available food is at a minimum. Lysis occur in which the nutrients remaining in the dead cells diffuse out to furnish the remaining cells with food (known as cryptic growth).

Growth in Mixed Cultures

Biological-treatment units are composed of complex, interrelated, mixed biological population, w/ each particular microorganism in the system having its own growth curve. The position and shape of a particular growth curve in the system, on a time scale, depend on the food and nutrients available and on environmental factors, such as temperature, pH, and whether the system is aerobic and anaerobic.

Bacterial Oxidation

The conversion of the organic matter to gaseous end products and cell tissue can be accomplished :

• aerobically• anaerobically• suspended-growth or attached-growth

systems

A portion of the organic material is oxidized to end products. This process is carried out to obtain the energy necessary for the synthesis of new cell tissue. In the absence of organic matter, the cell tissue will be endogeneously respired to gaseous end products and a residual to obtain energy for maintenance.

OxidationCOHNS + O2 + bacteria CO2 + NH3 + other end products + energySynthesis COHNS + O2 + bacteria + energyC5H7NO2 (bacterial cells)

(organic matter)

Endogenous respirationC5H7NO2 +5O2 5CO2 + NH3 +2H2O + energy